This research focuses on the development of the mammalian brain-pituitary-adrenal system. The chronically cannulated sheep fetus is the model used to study the ontogeny of the pituitary adrenal axis in utero while neonatal lambs are used for studying this axis postnatally. In addition to the in vivo experiments, results of in vitro studies on adrenal steroid responses to ACTH will be used to investigate possible mechanisms involved in changes in activity which occur during development.